The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Plant pathogens pose a unique challenge to the plant industry. The failure to control pathogens can result in significant crop losses. For example, Huanglongbing (hereinafter “HLB”) or Citrus greening disease is a serious threat to citrus production and an HLB infection can result in the loss of many trees.
Some have proposed methods of mitigating the damages of HLB using spray treatments. For example, Masaoka (US 2013/0259954) proposes using a liquid treatment containing Fe ions and at least some Fe ions in the form of Fe2+ ions. The liquid treatment can be sprayed onto leaves of citrus trees or poured on the roots of citrus trees that are infected by Citrus greening disease. In another example, Borras Hidalgo (EP 2681997) discloses a method of treating HLB through simultaneous activation of genes related to the route of salicylic acid, jasmonic acid/ethylene and hypersensitive response. Similar to Masaoka, the treatment can be applied via spray.
While some methods have disclosed spray treatments, other methods have also been used to delivery treatment to plants. For example, De Souza (US 2014/0024857) discloses using a cysteine amino-acid compound to control HLB by aiming to disrupt bacterial clusters in the phloem of the affected plant. The cysteine amino-acid compound can be applied as a drench (i.e., flooding a small area near the plant) or as a fertilizer in an encapsulated form. In another example, Wang (WO 2013/148677) discloses using SecA inhibiting compounds to affect protein translocation and potential signal peptide dependent virulence factors of Candidatius Liberibacter asiaticus (CLas), which is a causal agent of HLB. Compounds can be applied by conventional methods, such as dusting, sprinkling, brushing, dipping, smearing, impregnating, injection into the vascular system, and application to the root system.
Control of CLas in mature field trees using antimicrobial substances can be a promising tool in the fight against HLB. However, it is important to note that the success of antimicrobial treatments is intimately dependent on factors other than the efficacy of the antimicrobial agent itself. For example, two factors that affect the success of antimicrobial treatments include: (i) degree of antimicrobial penetration into the plant, and (ii) percent of uptake by phloem cells.
The problem with some of the methods described above is that the penetration of substances into the aerial parts of a plant is severely hindered by the presence of protective layers such as the cuticle (wax/cutin) on leaves and bark on stems. Although the primary functions of these protective covers are to guard against invading pests and to minimize water loss, the cuticle and bark also make formidable protective shields rendering penetration of externally supplied substances (e.g., spraying, drenching, sprinkling, etc.) virtually impossible.
Consequently, penetration of externally supplied substances into leaves is typically possible only through the stomata openings (found only on the abaxial side of citrus leaves) and through occasional cracks on the cuticle itself. Nevertheless, the collective surface area of stomatal openings that would allow for penetration of externally supplied solutions into the leaf is minimal, even under optimum conditions, since stomata often close under a variety of biotic and abiotic situations. Similarly, the bark, a complex tissue made up of dead suberized cork cells to the exterior and phloem cells to the interior, has very limited permeability through the cell wall fibrous material. Thus, the limited permeability of the cuticle and bark can be costly because more treatment may be needed to ensure enough absorption for the effective treatment of the plant. Additionally, using copious amounts of treatments can lead to pollution problems, which can greatly reduce soil quality.
Other methods of the delivery of a substance are disclosed in Eppstein (CA 2276312) and Watanabe (US 2005/0210744).
Thus, there is still a need for more efficient devices and methods for delivering substances to plants.